DentatoRubral and PallidoLuysian Atrophy (DRPLA) is a progressive neurodegenerative disease caused by a polyglutamine expansion in atrophin-1. The clinical features and areas of the brain affected resemble the more common Huntington's disease (HD), and we study the two diseases in parallel, since changes observed in both may represent common pathogenic features for all of the polyglutamine neurodegenerative diseases. In the previous grant period we generated a transgenic mouse model of DRPLA, and gathered some preliminary evidence suggesting the hypotheses that atrophin-1 undergoes proteolytic cleavage and nuclear translocation, resulting in gene transcription changes, as part of the pathogenesis of DRPLA. We gathered cell culture data to suggest that atrophin-1 has nuclear localization and export signals and that these are involved in toxicity. We now propose to conduct mechanistic in vivo experiments to test these ideas. In Specific Aim 1, we will generate transgenic mice expressing mutant full-length atrophin-1 with the putative nuclear localization signal altered, in order to determine whether nuclear localization contributes to pathogenesis in vivo. In Specific Aim 2, we will generate transgenic mice expressing mutant full-length atrophin-1 with the putative nuclear export signal altered, in order to determine whether nuclear localization contributes to pathogenesis in vivo. In Specific Aim 3, we will establish the site of cleavage of atrophin-1 with our collaborators at the Buck Institute, and generate mice transgenic for a construct expressing full-length atrophin-1 with this site altered. We will cross our atrophin-1 transgenic mice with mice hemizygous for a targeted deletion in the CBP gene in order to test the hypothesis that transcriptional misregulation contributes to pathogenesis in vivo. We predict that these experiments taken together will confirm roles in vivo for proteolytic cleavage, and nuclear localization, and support a role for alterations in gene transcription as critical for pathogenesis in DRPLA, and supporting the idea that these are general features of polyglutamine pathogenesis. Proteolytic cleavage would be an especially good target for therapeutic interventions. [unreadable] [unreadable]